The statistical analysis of censored disease incidence data in groups of animals subjected to a treatment depends on the designation of the disease as "lethal" or "non-lethal", the analysis being different for the two cases. In this research, a unified method is developed which makes use of information derived from incidental observations of the disease as well as deaths due to the disease. In particular, an extension of the Kaplan-Meier method is given for graphically summarizing the results for a single group. The same approach will be used to develop methods for comparing a treated group with a control, and, in particular, the estimation of relative risks for both the time to incidence of and the time to death from the disease.